Question

On Chatty Cathy’s cell phone plan she pays for minutes used plus a fixed monthly charge. For 500 minutes she pays $35 total, and for 1500 minutes used she pays $55 total.

What is her monthly fixed charge?

A) $15
B) $20
C) $25
D) $30

Answer 1

C) $25

Explanation:

$25 is correct. The slope of the line from (35, 500) to 55, 1500) is 20/1000 = .02, which is her cost per minute. Plug in one of the points into the equation y = mx + b to find b, which is the fixed cost.

Hope this helps

-Amelia

Answer 2

Answer: Option 'C' is correct.

Explanation:

Let the fixed monthly charges be x

Let the charges per minutes be y

According to question, we have

`x+500y=\$35\\x+1500y=\$55`

Now, by using the method of substitution for solving the system of linear equation:

`x=35-500y\\\\\text{ put in second equation i.e.}x+1500y=\$55\\\\35-500y+1500y=55\\\\35+1000y=55\\\\1000y=55-35\\\\1000y=20\\\\x=(20)/(1000)\\\\x=(1)/(50)`

Now, put the value of y in x , so we get,

`x=35-500y\\\\x=35-500*(1)/(50)\\\\x=35-10=\$25`

Hence, the monthly fixed charge is $25

Thus, Option 'C' is correct.